Methods and systems for generating energy from falling water are known in several forms, the most common being hydroelectric dams which seek to capture energy from rivers as the water they carry responds to the downward pull of gravity.
Another method known in the art is a “pump-back” lake, which is actually two lakes separated by a vertical distance. During times in which electricity is in higher demand or when electricity is sold for a greater value, water from the upper lake is released through a hydroelectric dam to the lower lake to generate electricity, which is sold at the higher value or used to supplement the peak demand for energy. Then, when demand is lower or energy prices are lower, electricity is purchased to pump water from the lower lake back up to the upper lake, thereby “reloading” the upper lake to generate electricity during the next peak demand or peak value period. The net value of this system is the difference between the higher value of electricity at the peak demand period and the lower value of electricity at the lower demand period. Most of the water, except for loss via evaporation and absorption, is conserved throughout the process.
Several other methods and systems for generating power as water falls through a building are also known or proposed. In one system, rain water is collected from the top of tall buildings, and directed through downspouts through turbines which generate electricity, and finally into the rain sewer system. Similarly, water may be collected from gray sources, such as showers and clothes washers, and optionally from black sources, such as toilets, and directed through turbines to generate power before it is finally disposed into a sanitary sewer. Each of these approaches uses turbines, which essentially consist of impellers or fan blades over which the falling liquid and contaminants it carries pass, thereby converting a portion of the kinetic energy of the falling liquid and solids into rotational energy which can be directed to an electrical generator.